The inventive concept relates to semiconductor memories, and more particularly, to a nonvolatile memory device.
A semiconductor memory device is a memory device which is embodied using a semiconductor such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phosphide InP, etc. A semiconductor memory device may be classified into a volatile semiconductor memory device or a nonvolatile semiconductor memory device.
A volatile memory device loses its stored data when its power supply is interrupted. Examples of the a volatile memory device include a static RAM (SRAM), a dynamic RAM (DRAM), a synchronous DRAM (SDRAM), etc. A nonvolatile memory device retains its stored data even when its power supply is interrupted. Examples of a nonvolatile memory device include a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory, a phase change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), etc. A flash memory may be classified into a NOR type flash memory or a NAND type flash memory.
To improve the integration of a semiconductor memory, a three-dimensional semiconductor memory device having a three-dimensional array structure is being studied. A height of a three-dimensional semiconductor memory device being stacked is a growing trend. As the height being stacked increases, a distance from a substrate becomes different depending on a location within a NAND string. Thus, a string select line or a ground select line being floated in an erase operation may be placed in various erase bias environments.